1. Field of the Invention
The present invention relates to a medical dressing comprising a complex of silver and being capable of releasing antimicrobial silver ion activity to a wound, a method for preparing such dressing, and a method for treating a human being.
The antiseptic activity of silver compounds is a well-known property, which has been utilised for many years. The bacteriostatic and fungistatic effect is caused by the silver ion and a simple compound, which has been used clinically, is for instance silver nitrate. Silver nitrate in concentrations of 0.5-1% in water shows disinfectant properties and is used for preventing infections in burns or for prophylaxis of neonatal conjunctivitis. For another silver compound, silver sulfadiazine, the antibacterial effect of the sulfadiazine molecule is further enhanced by the complexing with the disinfecting silver ion. In contrast to the silver nitrate, the solubility of the silver sulfadiazine complex is low and hence, both of the two active parts are only present in solution in low concentrations but may be present over a longer period of time before being washed out at site to be treated. The silver sulfadiazine is intensively used in the treatment of wounds, in particular burns, under the trademarks Silvadene® and Flamazine®. Silver-protein-combinations are yet other antiseptic formulations, which have been used, in low concentrations as eye drops.
2. Description of the Related Art
Antiseptics based on the silver ion are further used in various medical devices. One example of such application is the use in the wound dressing sold by Johnson & Johnson under the trademark Actisorb® which is an activated charcoal cloth dressing. Another example is the wound dressing sold under the trademark EZ-Derm by Genetic Laboratories which dressing is a modified pigskin impregnated with a soluble silver compound intended for treatment of burns.
A number of patents disclose compositions or devices showing antiseptic properties based on contents of silver compounds. EP 272 149 B1 discloses a medical dressing of the ‘hydrocolloid’ type containing and releasing active components. Silver chloride is a specific antiseptically acting compound mentioned in this patent.
EP patent publication No. 0 905 289 discloses antibacterial cellulose fibre being characterised in that a tertiary amine N-oxide was used as a solvent for pulp, and a silver based antibacterial agent selected from the group of silver zeolite, silver zirconium phosphate, silver calcium phosphate, and silver soluble glass. It is claimed that adding magnetized mineral ore powder may increase the antibacterial effect.
A specific advantage in using the silver ion as antiseptic agent is the general lack of formation of bacterial tolerance to the compound. This is in contrast to many types of antibiotics. However a major drawback when using ionic silver for bacteriostatic purposes is the reduction of the ion to free silver, which results in dark staining.
In the treatment of chronic wounds it is desirable to have a product capable of absorbing wound fluid and, at the same time also releasing antimicrobial activity to the wound bed. Burns, leg ulcers, diabetic foot ulcers and pressure sores may have delayed or slowed healing due to colonisation of the wound bed. For this purpose, it is desirable to have a dressing being able to absorb wound exudates and at the same time releasing antimicrobial activity to the wound, to prevent infection and/or delayed wound healing due to colonisation of the wound.
It is an object of the present invention to provide medical dressings capable of rendering silver ions available sufficiently quickly and in a sufficiently high and lasting concentration to ensure that an effective antiseptic activity is obtained and to ensure that the silver ions will not be released unintendedly from the dressing.
Still further it is an object to provide a method for preparing such medical dressings without losing the antiseptic activity of the silver ions.
Such medical dressings may e.g. be wound dressings, ostomy appliances or dressings for covering sites of the skin having an incision, e.g. for a catheter such as a catheter for drainage purposes.
It has surprisingly been found that certain silver complexes comprising silver and a transitional element of group IV of the Periodic System of Elements may be incorporated in an adhesive or foam matrix of a medical dressing without loosing the antiseptic activity and that the release of silver ions may be controlled to ensure that silver ions will not be released from the dressing unintendedly and that the release may be initiated in a controlled manner.